The present invention relates to a device and a procedure for the quality control of in particular finished surfaces. In numerous products, the quality or the visual properties of its surface become an important characteristic for the overall appearance of the product. Thus, in order to achieve a high reproducibility during production, retouching or repair work on objects, quality control measurements are carried out on the products to determine one or several parameters (such as for example: color, gloss, haze, orange peel, etc.).
Particularly with finished surface""s, but not limited solely thereto, their visual properties may change depending upon viewing angle, respectively angle of illumination. Such surfaces are called goniochromatic.
Examples of such surfaces are those with effect, metallic or pearl lustre finishes, coated surfaces as well as interference color surfaces, or even synthetic surfaces having inlaid transparent particles and other such similar surfaces.
Finished surfaces having inlaid metal particles may exhibit, for example, FLOP effects so that a change in color dependant upon the viewing angle may be observed. Such effects may be induced, for example, by aluminum particles inlaid in the surface and which then act as mirrors.
In order to offer consumers products featuring new colors, new finishes are developed which are able to exhibit specific qualities.
In many effect finishes, there is a particular viewing angle at which a change in parameters occurs. Should a surface be observed at a slightly lesser angle, a first impression of color may, for instance, be noted, while a second impression of color, which may conceivably differ considerably from the first impression of color, may be noted upon scanning or measuring at a slightly greater angle.
Measuring devices which illuminate a measurement surface at an angle and which measure the reflected light at two fixed angle ranges in order to determine the color of a surface to be examined under these two scanning angles are known from the prior art. Furthermore, goniometric measuring devices are also known in the prior art with which, for example, a surface is illuminated at a fixed angle and a photosensor is trammed across the entire angle range in order to obtain the surface color as a function of the scanning angle.
However, goniometric devices have the disadvantage that in order to determine color function, the sensor must be trammed over the entire angle range during each measurement and a mechanical decalibrating of the device cannot always be excluded.
It is the task of the present invention to provide a device and a procedure of the type as indicated above to enable a quality control of surfaces and finished surfaces in particular.
Another aspect of the task of the present invention is to provide a device which can determine at least one visual property of a surface, including of those surfaces which may also have been given new finishes or other such similar treatments.
This task is solved in accordance with the present inventive device and method as described herein.
Preferred embodiments of the invention constitute the subject matter of the subclaims.
A device according to the present invention for the quality control of especially finished surfaces comprises an illuminating means having at least one light source. The light radiated from said illuminating means is directed to the measurement surface at a predetermined angle. A plurality of at least three, preferably at least five measuring means are furthermore provided, which each receive at least a portion of the light reflected by the measurement surface. Each measuring means has at least one photosensor which emits at least one electrical measurement signal, whereby said electrical measurement signal is characteristic of the light received by the measuring means.
The inventive device furthermore has at least one control and evaluation means provided with at least one processor and at least one memory means in order to control the measurement sequence, evaluate the measurement results, and derive a parameter from the measurement signals which characterizes the surface. An output means serves to display, respectively forward, the measurement results.
The device according to the present invention has numerous advantages:
Arranging each of the plurality of measuring means in the inventive device at a different angle to the measurement surface enables the evaluation means to derive a parameter which is characteristic of the surface from the measurement signals of the individual measuring means.
Preferably at least one characteristic parameter is determined for the measured surface; this parameter may be its color, gloss, haze, orange peel or distinction of image. It is moreover possible that two or three different parameters can be determined and/or that, for example, at least one parameter each may be determined from respectively two, three or all measuring means.
Especially preferred is determining the color parameter of the measurement surface whereby it is possible that a set of color characteristics are determined in that, for example, each measuring means determines one color characteristic. In a preferred embodiment of the invention, a plurality of retaining means are provided in the device upon each of which a measuring means is disposed. Especially preferred is that the number of retaining means is greater or identical to the number of measuring means so that, for example, ten retaining means are provided whereby measuring means are disposed upon five of these ten retaining means.
A greater number of retaining means relative to the number of measuring means is highly advantageous because this enables changing the position of one measuring means from a first retaining means to a second retaining means upon which no other measuring means has been disposed.
With this type of device, the individual positions of the measuring means can be changed essentially at any time which enables the device to be adapted to changed conditions.
The retaining means serve to hold or support the measuring means, respectively parts thereof, and are preferably realized as conventional retaining means as known in the prior art.
In a preferred embodiment of the present invention, the angle spacing between at least three adjacent retaining means is in each case identical and especially preferred is that essentially all the angle spacings of adjacent retaining means are essentially identical. For example, more than 30 retaining means are disposed across a 180xc2x0 range of angles in the present embodiment, the spacings between said means in each case amounting to 5xc2x0, whereby a greater angle spacing can also be given between a first area of the retaining means and a second area of the retaining means. It is likewise possible that the aggregate of retaining means are distributed across, for example, three angle ranges in that the angle spacings from one to the next are identical, whereby greater angle spacings are found between the individual areas.
This embodiment is particularly advantageous. Positioning the retaining means for instance at a 3xc2x0 or 5xc2x0 spacing from one another enables setting the angle at which a measuring means receives a portion of the light reflected from the surface at small increments. Should the retaining means be arranged during the actual manufacturing of the device, a measuring means can be brought from one retaining means onto another retaining means with relatively low expenditure.
In a preferred embodiment of the present invention, at least one measuring means comprises an optical photoconductor means and a spectral means, whereby the optical photoconductor means receives a portion of the light reflected from the measurement surface and conveys same to the spectral means. In this embodiment, the predetermined angle at which the measuring means is directed to the measurement surface corresponds to the angle at which in this case the optical photoconductor means is directed to the measurement surface, while parts of the measuring means, such as for example the spectral means, may then be aligned at any chosen angle. The disposing of optical photoconductor means in at least one measuring means (preferably in essentially all measuring means) is of great advantage as this enables the providing of a small optics block in the device which is the size of, for example, a matchbox or a paperback book. This in turn keeps the overall size of the device small enough so that it can be used portably by the user.
In a preferred embodiment of the present invention, at least two, preferably essentially all the measuring means, receive essentially simultaneous measurement signals during the measurement of the surface, fundamentally ruling out any distortions in the measurement results such as those due to, for example, temporal fluctuations in the radiated light intensity of the illuminating means. This embodiment has the further advantage of reducing the overall measurement time required since the light received can be analyzed concurrently in the various measuring means.
In another preferred embodiment of the present invention, at least two, preferably all of the measuring means receive the measurement signals basically one after the other. A configuration of this type grants the advantage that the intensity of surface illumination can be varied for the individual measuring means so that, for example, the intensity of illumination can be increased for measurements employing measuring means arranged at an angle to the surface at which only low light is reflected, while inversely the intensity of illumination can be decreased for those measuring means arranged at angle ranges at which a great deal of light is reflected. This enables operating the sensors at a consistently high dot resolution so that a high signal-to-noise ratio may be obtained.
In a further preferred embodiment of the present invention, a filter means is arranged in the path of radiation between the light source and at least one photosensor. The filter means changes the spectral characteristics of the incident light according to the specific filter properties in such a manner that a spectral characteristic of the conveyed light approaches that of a predetermined spectral distribution.
Utilizing of a filter means enables the spectral distribution of the light used for the measurement to be adapted to specific stipulations.
In a further preferred embodiment of the present invention, said predetermined spectral distribution is a standard distribution which exhibits a constant intensity, for example in at least one wavelength band, or a distribution which exhibits, for example, the C light type standard, the D65 light type standard, the A light type standard or other such similar standards. A measurement conducted can thus be illuminated, respectively measured, directly under standard conditions.
In another preferred embodiment, a spectral measurement characteristic is proportional to a predetermined spectral distribution, wherein same may correspond, for example, to a constant value across the relevant wavelength band or to a Gaussian distribution or to the spectral visual sensitivity of the human eye. The spectral measurement characteristic is thereby determined as a product of the measurement surface incident light and the spectral sensitivity of the photosensor.
The adaptation of the spectral distribution or the spectral measurement characteristics to predetermined spectral distributions is highly advantageous. When the spectral distribution is adapted to the sensitivity of the human eye, it is then possible to adapt measurement conditions to the average human being. On the other hand, if the spectral measurement characteristic is adapted to an essentially constant spectral distribution, measurement accuracy is increased since a higher signal-to-noise ratio is obtained.
In a preferred embodiment of the present invention, the illuminating means has at least two light sources, whereby said light sources are configured preferably as conventional light sources as known in the prior art. It is possible to use, for example, conventional or halogen light bulbs, fluorescent and/or semi-conductor light sources. It is especially preferred for at least two of the light sources of said illuminating means to exhibit a different spectral characteristic. The second light source may then emit light, for example particularly in those bands of radiation in which the first light source emits at only low intensity or none at all, so that the spectral distribution of the intensity of radiation of both light sources exhibits less pronounced minima. Especially preferred when utilizing at least two light sources is that at least one of said light sources is a light-emitting diode. The use of light-emitting diodes as light sources in the illuminating means is highly advantageous since light-emitting diodes are subject to less aging than conventional thermal sources of radiation and since they continue to radiate at a relatively stable light intensity over time. In another preferred embodiment of the present invention, a control measuring means is provided in the illuminating means which is fed, at least intermittently, a part of the light emitted from the illuminating means. Since fluctuations in light intensity can be taken into account, a control measuring means which determines a standard gauge for the light emitted from the illuminating means allows for increasing the reproducibility of the measurement.
In a preferred embodiment of the present invention, at least one photosensor (preferably all) has a number of photosensitive elements which are preferably arranged adjacent to one another. Especially preferred is the configuration of a row of photodiodes or a CCD array. It is highly advantageous, particularly when utilizing spectral means in the measuring means, to provide a plurality of photosensitive elements on one or on each photosensor, since the spectral means can then split the received light according to wavelength and thus feed light of different wavelengths to the individual photosensitive elements of the photosensors so that the spectral distribution of the received radiation can be determined.
Especially preferred is the configuring of the spectral means of the measuring means as diffracting optical elements, whereby same may be configured as transmitting as well as also reflecting elements.
In a further preferred embodiment of one or all of the previously described embodiments, at least one temperature measuring means is disposed in immediate proximity to at least one light source and/or at least one photosensor, provided for determining the characteristic temperature of each respective light source, respectively photosensor, in order to enable a temperature-corrected determination of said at least one parameter.
Especially preferred in this case is that one or several photosensors are disposed with such a temperature measuring means so as to grant increased measurement reproducibility and accuracy by means of the temperature-corrected determination of the measurement results.
The temperature measuring means can hereby particularly also be the electric component itself, especially with semi-conductor components such as conventional photosensors. This enables deriving the component""s temperature from the determination of open-circuit voltage, amperage or other electrical characteristic. Using such a component itself to determine its temperature is highly advantageous because due to the slight time difference between temperature measurement and light measurement (respectively as regards light sources, between the temperature measurement and the light radiation), such a determination is very reliable as there is no, or only negligibly slight thermal capacities to distort the determination of temperature in dynamic processes.
The inventive procedure makes use of one of the previously described configurations of the measuring device having a plurality of measuring means, whereby adjacent measuring means preferably have the same angle spacing to one another. Said device is provided with preferably at least ten, especially preferred with up to 60 or more measuring means, each aligned at different predetermined angles to the measurement surface.
The inventive procedure is utilized preferably for the determining at least of one, preferably two, three, four, five or more scanning angles of a surface type.
When measuring with a first measuring device which is preferably designed especially for laboratory operation, parameters can be determined for the surface to be examined from a number of angles. By evaluating said plurality of parameters, typically one, two, three or more scanning angles can be determined which characterize the surface type to be examined.
In the case of so-called effect finishes, these are for example a nacreous or a FLOP effect angle, meaning an angle at which, for example, a color change is observable.
In addition to the determining of at least one characteristic angle for the surface type to be examined, a measuring means is disposed in a second measuring device at a specific angle respective said first measuring means, respectively a measuring device is built to realize this angle.
Preferably, the first measuring device (laboratory device) selects at least three different angles in the inventive procedure and transmits same to the second measuring device (field measuring device), so that three different measuring means are aligned in said second measuring device at the corresponding angles.
In a preferred embodiment of the inventive procedure, the second measuring device has a plurality of retaining means, said plurality being greater than the number of measuring means in the second measuring device. It is preferable that the angle spacing between adjacent retaining means is essentially the same. Subsequent to the determining of a characteristic angle with the first measuring device, the measuring means of the second measuring device may then be brought into the corresponding position.
In a preferred embodiment of the inventive procedure, the arrangement of the retaining means of the second measuring device (field measuring device) is identical to the arrangement of the retaining means in the first measuring device (laboratory device).
It is preferred that the field measuring device encompasses essentially identical optical conditions as in the laboratory device. This ensures a simple transferability of the geometrical relationships and enables the attaining of a high reproducibility to the measurement results. The retaining means of the hand-held or field measuring device may also be configured differently from the retaining means of the laboratory device. It is likewise also possible that the illuminating means and the measuring means of the handheld measuring device are not identical to those of the laboratory device since greater demands are often placed on laboratory measuring devices, for example with respect to precision.
It is likewise particularly preferred that the optics block on which the retaining means are arranged is essentially the same in both measuring devices, whereby the production tolerance for the first measuring device may be more exacting than the production tolerance for the second measuring device.
A further advantage of the inventive measuring device is that essentially no movable elements are used in said measuring device.